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BCR405U Datasheet(PDF) 1 Page - Infineon Technologies AG |
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BCR405U Datasheet(HTML) 1 Page - Infineon Technologies AG |
1 / 8 page AN 066 Rev D 1 / 8 16-Jan-2004 Applications Note No. 066 Silicon Discretes BCR402R: Light Emitting Diode (LED) Driver IC Provides Constant LED Current Independent of Supply Voltage Variation • Supplies stable bias current for Light Emitting Diodes (LEDs) • Low Voltage Drop of 0.75V maximizes system DC efficiency • LED drive current adjustable via single external resistor (20 – 60 mA range) • Negative temperature coefficient protects LEDs against thermal runaway • Low Cost, Low External Parts Count, Easy-to-Use, Fast Time-To-Market • Small Surface-Mount SOT143R packaging (2.9 x 1.6 x 1.1 mm inc. leads) 1. Introduction Light-Emitting Diodes (LEDs) and LED displays suffer from varying illumination levels as a result of changes in power supply voltages. This is true for displays used in automotive applications, battery-operated handheld devices, or fixed (architectural) installations. To keep LED brightness constant, it is necessary to stabilize the LED’s current over the anticipated power supply voltage variation range. Often a resistor in series with the LED(s) is used to stabilize current. However, this method has some serious drawbacks. To achieve good LED current stability over the varying supply voltage range, the resistor must take on a large value (infinite resistance, in the ideal case) to make the power supply plus series resistor combination approach the traits of an ideal constant current source having infinite output impedance. In such cases, there is a large voltage drop across this series resistor. For a particular supply voltage, this voltage drop 1) reduces the number of LEDs that can be driven by one resistor, requiring additional parallel resistors with which to drive a given number of LEDs, thereby increasing system current consumption and 2) power is “burned” or wasted as heat in these series resistors. Infineon’s LED driver family, consisting of the BCR401R, BCR402R, BCR402U and BCR405U, offers an easy, cost-effective and reliable way to achieve LED current stabilization while overcoming the drawbacks inherent in using a series resistor. These LED driver IC’s cover the most commonly used LED supply current ranges – 10mA, 20mA, and 50mA. Refer to Figures 1 and 2. In each device, the nominal drive current may be easily adjusted upward from the nominal value by adding a single external resistor – for BCR401R / 402R, connect this resistor between pins 3 and 4. Figure 1. Infineon LED Current Driver Family Recommended Current Ranges. Device Package Recommended Current Range Maximum Power Dissipation BCR401R SOT143R 10 – 60 mA 330 mW * BCR402R SOT143R 20 – 60 mA 330 mW * BCR402U SC74 20 – 65 mA 500 mW ** BCR405U SC74 50 – 65 mA 500 mW ** * Soldering Point Temperature TS = 87 °C ** Soldering Point Temperature TS = 117 °C For selecting the proper resistor value to increase BCR402 drive current above the nominal level of 20mA, refer to Figure 3, which |
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